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Seafood Watch Seafood Report
Farmed Scallops
(Illustration © Monterey Bay Aquarium Foundation)
Final Report July 20, 2006 Aaron A. McNevin, Ph.D. A.A. McNevin & Associates
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
About Seafood Watch® and the Seafood Reports Monterey Bay Aquarium’s Seafood Watch® program evaluates the ecological sustainability of wild-caught and farmed seafood commonly found in the United States marketplace. Seafood Watch® defines sustainable seafood as originating from sources, whether wild-caught or farmed, which can maintain or increase production in the long-term without jeopardizing the structure or function of affected ecosystems. Seafood Watch® makes its science-based recommendations available to the public in the form of regional pocket guides that can be downloaded from the Internet (seafoodwatch.org) or obtained from the Seafood Watch® program by emailing [email protected]. The program’s goals are to raise awareness of important ocean conservation issues and empower seafood consumers and businesses to make choices for healthy oceans. Each sustainability recommendation on the regional pocket guides is supported by a Seafood Report. Each report synthesizes and analyzes the most current ecological, fisheries and ecosystem science on a species, then evaluates this information against the program’s conservation ethic to arrive at a recommendation of “Best Choices”, “Good Alternatives”, or “Avoid”. The detailed evaluation methodology is available upon request. In producing the Seafood Reports, Seafood Watch® seeks out research published in academic, peer-reviewed journals whenever possible. Other sources of information include government technical publications, fishery management plans and supporting documents, and other scientific reviews of ecological sustainability. Seafood Watch® Fisheries Research Analysts also communicate regularly with ecologists, fisheries and aquaculture scientists, and members of industry and conservation organizations when evaluating fisheries and aquaculture practices. Capture fisheries and aquaculture practices are highly dynamic; as the scientific information on each species changes, Seafood Watch’s sustainability recommendations and the underlying Seafood Reports will be updated to reflect these changes. Parties interested in capture fisheries, aquaculture practices and the sustainability of ocean ecosystems are welcome to use Seafood Reports in any way they find useful. For more information about Seafood Watch® and Seafood Reports, please contact the Seafood Watch® program at Monterey Bay Aquarium by calling (831) 647-6873 or emailing [email protected]. Disclaimer Seafood Watch® strives to have all Seafood Reports reviewed for accuracy and completeness by external scientists with expertise in ecology, fisheries science and aquaculture. Scientific review, however, does not constitute an endorsement of the Seafood Watch® program or its recommendations on the part of the reviewing scientists. Seafood Watch® is solely responsible for the conclusions reached in this report. Seafood Watch® and Seafood Reports are made possible through a grant from the David and Lucile Packard Foundation.
1
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Executive Summary Scallop culture of 1.2 million metric tons (mt) was 10% of the total bivalve production by world aquaculture in 2003. Scallops have a broad, worldwide distribution and can be cultured in many countries. Approximately 96% of the scallops consumed in the United States are captured from the wild and most of these are from domestic U.S. fisheries; the rest are wild-caught product imported from Canada. Although only about 4% of scallops consumed domestically are farmed, nearly all of these are imported from China and Japan. Scallop spat for aquaculture are captured from the wild with spat collectors or produced in hatcheries and transplanted to sites in coastal waters for grow-out. Culture is by either offbottom or on-bottom methods where scallops are suspended in the water column or laid on the seabed, respectively. Scallops produced by on-bottom techniques usually are harvested by dredging, while scallops produced by off-bottom techniques scallops are harvested by hand. Dredging of scallops from on-bottom culture plots can have negative impacts on the seabed and cause benthic diversity to decline. Fertilizers and feeds are not applied at grow-out sites for scallops, so nutrient additions do not occur. Antibiotics, drugs, and other chemicals used in some other kinds of aquaculture for disease control are seldom used in scallop grow-out activities. Scallops are filter feeders and remove particulate matter from water. Thus, they remove organic matter and nutrients from the water column and can improve water quality. Scallops also remove viral and bacterial particles from the water and thus can accumulate algal toxins, pesticides, heavy metals, and other toxic substances. Scallops cultivated at polluted sites or in waters with toxic algal blooms may be contaminated with disease organisms or toxins. The capture of wild scallop spat for use in aquaculture does not appear harmful to natural scallop populations because spat are transplanted to sites that are generally superior to those where spat would settle naturally. However, caution is raised for cultured scallops in China when wild spat are collected, because of the generally low abundance of scallops in the wild. Due to the lower impacts of farmed scallops produced by off-bottom techniques, off-bottom scallops are ranked Best Choice, while on-bottom scallops, which are dredged, are a Good Alternative when suspended culture scallops are not available.
2
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Table of Sustainability Ranks Sustainability Criteria
Low
Use of Marine Resources
√
Risk of Escaped Fish to Wild Stocks Risk of Disease and Parasite Transfer to Wild Stocks Risk of Pollution and Habitat Effects Management Effectiveness
√
Conservation Concern Moderate High
Critical
√ China, using wild-caught spat
√ √ off-bottom
√ dredged √ China and Japan
About the Overall Seafood Recommendation • • •
A seafood product is ranked “Avoid” if two or more criteria are of High Conservation Concern (red) OR if one or more criteria are of Critical Conservation Concern (black) in the table above. A seafood product is ranked “Good Alternative” if the five criteria “average” to yellow (Moderate Conservation Concern) OR if four criteria are of Low Conservation Concern (green) and one criteria is of High Conservation Concern. A seafood product is ranked “Best Choice” if three or more criteria are of Low Conservation Concern (green) and the remaining criteria are not of High or Critical Conservation Concern.
Overall Seafood Recommendation Off-bottom scallops: Best Choice
Good Alternative
Avoid
Good Alternative
Avoid
On-bottom (dredged) scallops: Best Choice
3
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Introduction Most concerns about the possible negative environmental impacts of aquaculture have focused on culture of freshwater and marine fish in cages, flow-through systems, and ponds, and the production of marine shrimp in ponds (Goldburg and Triplett 1997; Naylor et al. 2000). There has been much less discussion of the potential negative effects of the culture of bivalve shellfish as a result of the comparatively low impacts of producing them. Bivalves are filter feeders that obtain their nutrition by removing suspended particles from water. Because it is not necessary to apply feeds to stimulate production, bivalve farming does not increase nutrient inputs to coastal waters. In fact, an increase in abundance of shellfish in an area is usually considered to have a positive benefit on water quality (Shumway et al. 2003). Bivalve aquaculture includes the production of oysters, clams, mussels, and scallops. Statistics from the United Nations (UN) Food and Agriculture Organization (FAO) reveal that scallops are a popular seafood item and the harvest of scallops from the sea cannot meet the demand. The culture of these organisms increased from 975,000 metric tons (mt) in 1993 to nearly 1.2 million mt in 2003, to account for about 59% of world scallop production. Shumway et al. (2003) discussed the environmental virtues of bivalve culture in comparison to other types of aquaculture. They state that bivalve aquaculture has great potential for increasing seafood production without causing negative environmental impacts. Scallops are an expensive and increasingly-popular member of the bivalve group. There is rapid expansion of the scallop aquaculture industry and as demand grows, production practices in countries from which the United States imports need to be better understood. Basic biology Scallops are of the class Bivalvia, order Pterioida, and family Pectinidae. There are more than 360 species of scallops worldwide, and approximately 15 of these are used for aquaculture (Spencer 2002). Proportions of cultured scallop species produced globally are presented in Figure 1.
Figure 1. Global proportions of the main scallop species produced by aquaculture. Source: FAO 2005.
4
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
In the bay scallop (Argopecten irradians) (Figure 2), the labeum is situated at the end of the gill and is composed of a pair of labial palps on each side. The mouth appears to be split in the center of two labial palps and is connected to the esophagus. The flat oval-shaped stomach is connected to the esophagus at its upper end and to the intestine and rectum at its lower end. The rectum passes through the ventricle and goes downward along the back of the adductor muscle and turns to form the anus. The crescent-shaped gonad usually is located between the posterioventral part of the foot and the front side of the adductor muscle.
Figure 2. The bay scallop (Argopectens irradians). Image credited to Tampa Bay Watch.
Food is filtered by the gills and then sent to the mouth by movement of the labial palps. Food ingested by scallops is composed of phytoplankton, zooplankton, bacteria, and detritus. Under normal living conditions, the two shells of a feeding scallop are slightly open and the tentacles on the edge of the mantle are extended. If environmental conditions become unsuitable, the young scallop is capable of cutting off its byssus and swimming to a better location by means of a water-jet generated by the closing and opening of its shells. Scallops can swim faster than any other species of bivalves. When it finds a suitable place, it secretes a new byssus and attaches to the substratum again. The ability to secrete the byssus is determined by the size of the scallop and the water temperature. After it has grown up, the bay scallop discards its byssus. Scallops usually discharge sperm before releasing eggs. Mature sperm are smaller than eggs and swim actively in seawater where fertilization takes place. The embryo gradually develops into a free-swimming, ciliated larva called a veliger. During this stage the shell is secreted and the larva becomes a D-shaped pediveliger. At this stage, the larvae (often called crawlers) have both a functional velum and a foot, and alternately swim about and crawl on the bottom or other substratum. After a few days of crawling, the swimming ability of larvae gradually is reduced until the velum is completely reabsorbed and they must settle. Once settled, organs such as foot, velum and eye spot degenerate, and the gill and adductor muscles develop quickly. The early developmental stages of scallops are depicted in Figure 3.
5
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Figure 3. Developmental stages of the bay scallop (Argopecten irradians). Image credited to the Florida Fish and Wildlife Conservation Commission.
Aquaculture production Aquaculture has become a more important source of scallops than wild catch in many countries (Figure 4). According to FAO (2005), scallops are currently produced in 20 countries, the leading producer of which is China, followed by Japan, Chile, and Peru (Figure 5). China has in the past been the major producer of all types of bivalves, but Japan has provided most of the major advances in scallop aquaculture technology. Chile and Peru have been diversifying their aquaculture production since the late 1970s, and scallops have proven to be a profitable export.
Production (mt x 100,000)
25 Aquaculture Capture
20 15 10 5 0 1991
1994
1997
2000
2003
Figure 4. Comparison of scallop aquaculture and wild capture of scallops. Source: FAO 2005.
The two most valuable species of scallops produced in China are the Zhikong scallop (Chlamys farreri), which is native, and the Yesso scallop (Patinopectin yessoensis). The Zhikong and Yesso scallops are cultured in cool waters of the Bohai and Yellow Seas in northern China, while 6
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
to a lesser degree the bay scallop is cultured in warmer waters along the mid section of China’s coastline. The Yesso scallop was transplanted from Japan to China and the bay scallop is native to North America. Culture of these species using wild-caught seed and Japanese technology began in the 1960s (Spencer 2002). Scallop culture increased and hatcheries were introduced to enhance the spat supply. From 1993 to 2003, scallop production in China increased five-fold, though during that time period there were dramatic fluctuations in production. For example, production decreased from 1,000,000 mt in 1997 to 629,000 mt in 1998 as the result of mass mortalities during the summer. Gosling (2003) attributed these die-offs to over-crowding, high water temperatures, and deteriorating water quality. In Japan, the central government has provided significant funding for the advancement of scallop aquaculture. Japanese scallop farming dates back to 1936 in North Hokkaido; however, scallop farming was not successful until the late 1960s. The main species cultured in Japan is the Yesso scallop. Initially, only bottom culture was conducted along the coast of Hokkaido, and presently bottom culture still accounts for over half of the production in this area. Suspended culture of scallops is common in Mustso Bay in northern Aomori. Ear-hanging of scallops was very popular in the 1980s, but production by this technique has declined because of excessive fouling. Scallop production in Japan also fluctuated during the period 1993 to 2003. Production peaked at 265,000 mt in 1996 and then decreased annually until it reached 210,000 mt in 2000. Production increased in 2003 to 258,000 mt. The main culture species in Chile is the Chilean/Peruvian scallop (Argopecten purpuratus). The scallop industry in Chile was established in the late 1970s, and it has become a profitable component of the nation’s aquaculture industry. Much of the production in Chile has been aided by Japanese overseers. The main areas of production are the Mejillones, Tongoy, and Herradura Bays in northern Chile. Spatfalls are irregular and the country is reliant on hatcheries for spat. Grow-out of spat to market size is conducted using Japanese lantern nets and ear-hanging techniques. The Chilean scallop industry produced a high of 21,000 mt in 1999, but production declined to 15,000 mt in 2003. Production in Chile has been hindered by insufficient spatfalls and excessive fouling.
7
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Production (mt x 10,000)
140 120 100
China Japan Chile Peru Others
80 60 40 20 0 1991
1994
1997
2000
2003
Figure 5. The major countries producing scallops by aquaculture. Source: FAO 2005.
Peru’s scallop industry developed from the natural fishery. Divers retrieving scallops for sale sold undersized scallops to farmers for further grow-out. This progressed to the adoption of traditional scallop culture in Peru. The main species produced in Peru is Argopecten purpuratus. Seed is obtained from the wild using spat collectors, and grow-out is performed using hanging culture techniques. Peruvian scallop farming is centered on the Bay of Paracas where the seabed is leased from the Department of Fisheries and the Department of Navy. The Peruvian industry has grown more slowly than that of other major scallop-producing countries. Production in Peru was between 100 and 500 mt during the period 1993-1997. Production has increased, and in 2003, about 6,700 mt of scallops were produced. The increase in production can be attributed to refinement in culture techniques. Moreover, a higher price can be obtained for Peruvian scallops when there is low capture of the Calico scallop (Argopecten gibbus) in Florida. The global value of scallops reached $1.8 billion in 1997 (Figure 6), but declined drastically in 1998 as a result of the decreased production in China. Since 1998, the value of scallops from aquaculture has continued to increase each year and was $1.7 billion in 2003.
8
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Value (USD x billions)
2.5 2.0 1.5 1.0 World Scallop Value
0.5 0.0 1992
1994
1996
1998
2000
2002
2004
Figure 6. The economic value in billions of U.S. dollars (USD) of world scallop production. Source: FAO 2005.
FAO (2005) data reveals that there is relatively little production of scallops by aquaculture in the United States, but capture of scallops in U.S. waters is approximately 207,000 mt. Of this quantity roughly 7,000 mt is exported (FAO 2005). Thus, the U.S. consumes 200,000 mt of captured scallops from U.S. waters and 23,580 mt from imports, which include a combination of cultured and wild-caught scallops. Data on the fraction of scallop imports produced by aquaculture internationally is not readily available, but estimates of this fraction can be calculated using a combination of U.S. trade data and FAO aquaculture and capture fisheries statistics (Table 1). From these estimates a rough idea of the quantity of scallops produced by aquaculture and by which country can be tallied. U.S. imports of scallops produced by aquaculture are estimated at 8,304 mt or roughly 35% of all scallops imported. Yet when compared to total scallops consumed in the U.S., scallops imported and produced by aquaculture represent only 3.7%. Thus, over 96% of all scallops consumed in the United States are captured from the wild. Although these estimates reveal that few farmed scallops are consumed in the United States, there is a fraction of scallop imports which are produced by aquaculture. The overwhelming majority of these imports originate in China and Japan (Table 1).
9
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Table 1. U.S. imports of scallops produced by aquaculture and country of origin for 2003 (USDA FAS 2005; FAO 2005). Percentage of aquaculture production calculated using FAO statistics on aquaculture and capture production of scallops for individual countries. Note: Quantity of scallop aquaculture imports estimated by fraction of individual countries’ percentages of scallop aquaculture and does not represent actual value of U.S. imports of scallops produced by aquaculture. U.S. scallop import quantity (mt)
Percentage of export country aquaculture production of scallops
Estimate of scallop imports by aquaculture (mt)
Australia
1
Farmed Scallops
(Illustration © Monterey Bay Aquarium Foundation)
Final Report July 20, 2006 Aaron A. McNevin, Ph.D. A.A. McNevin & Associates
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
About Seafood Watch® and the Seafood Reports Monterey Bay Aquarium’s Seafood Watch® program evaluates the ecological sustainability of wild-caught and farmed seafood commonly found in the United States marketplace. Seafood Watch® defines sustainable seafood as originating from sources, whether wild-caught or farmed, which can maintain or increase production in the long-term without jeopardizing the structure or function of affected ecosystems. Seafood Watch® makes its science-based recommendations available to the public in the form of regional pocket guides that can be downloaded from the Internet (seafoodwatch.org) or obtained from the Seafood Watch® program by emailing [email protected]. The program’s goals are to raise awareness of important ocean conservation issues and empower seafood consumers and businesses to make choices for healthy oceans. Each sustainability recommendation on the regional pocket guides is supported by a Seafood Report. Each report synthesizes and analyzes the most current ecological, fisheries and ecosystem science on a species, then evaluates this information against the program’s conservation ethic to arrive at a recommendation of “Best Choices”, “Good Alternatives”, or “Avoid”. The detailed evaluation methodology is available upon request. In producing the Seafood Reports, Seafood Watch® seeks out research published in academic, peer-reviewed journals whenever possible. Other sources of information include government technical publications, fishery management plans and supporting documents, and other scientific reviews of ecological sustainability. Seafood Watch® Fisheries Research Analysts also communicate regularly with ecologists, fisheries and aquaculture scientists, and members of industry and conservation organizations when evaluating fisheries and aquaculture practices. Capture fisheries and aquaculture practices are highly dynamic; as the scientific information on each species changes, Seafood Watch’s sustainability recommendations and the underlying Seafood Reports will be updated to reflect these changes. Parties interested in capture fisheries, aquaculture practices and the sustainability of ocean ecosystems are welcome to use Seafood Reports in any way they find useful. For more information about Seafood Watch® and Seafood Reports, please contact the Seafood Watch® program at Monterey Bay Aquarium by calling (831) 647-6873 or emailing [email protected]. Disclaimer Seafood Watch® strives to have all Seafood Reports reviewed for accuracy and completeness by external scientists with expertise in ecology, fisheries science and aquaculture. Scientific review, however, does not constitute an endorsement of the Seafood Watch® program or its recommendations on the part of the reviewing scientists. Seafood Watch® is solely responsible for the conclusions reached in this report. Seafood Watch® and Seafood Reports are made possible through a grant from the David and Lucile Packard Foundation.
1
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Executive Summary Scallop culture of 1.2 million metric tons (mt) was 10% of the total bivalve production by world aquaculture in 2003. Scallops have a broad, worldwide distribution and can be cultured in many countries. Approximately 96% of the scallops consumed in the United States are captured from the wild and most of these are from domestic U.S. fisheries; the rest are wild-caught product imported from Canada. Although only about 4% of scallops consumed domestically are farmed, nearly all of these are imported from China and Japan. Scallop spat for aquaculture are captured from the wild with spat collectors or produced in hatcheries and transplanted to sites in coastal waters for grow-out. Culture is by either offbottom or on-bottom methods where scallops are suspended in the water column or laid on the seabed, respectively. Scallops produced by on-bottom techniques usually are harvested by dredging, while scallops produced by off-bottom techniques scallops are harvested by hand. Dredging of scallops from on-bottom culture plots can have negative impacts on the seabed and cause benthic diversity to decline. Fertilizers and feeds are not applied at grow-out sites for scallops, so nutrient additions do not occur. Antibiotics, drugs, and other chemicals used in some other kinds of aquaculture for disease control are seldom used in scallop grow-out activities. Scallops are filter feeders and remove particulate matter from water. Thus, they remove organic matter and nutrients from the water column and can improve water quality. Scallops also remove viral and bacterial particles from the water and thus can accumulate algal toxins, pesticides, heavy metals, and other toxic substances. Scallops cultivated at polluted sites or in waters with toxic algal blooms may be contaminated with disease organisms or toxins. The capture of wild scallop spat for use in aquaculture does not appear harmful to natural scallop populations because spat are transplanted to sites that are generally superior to those where spat would settle naturally. However, caution is raised for cultured scallops in China when wild spat are collected, because of the generally low abundance of scallops in the wild. Due to the lower impacts of farmed scallops produced by off-bottom techniques, off-bottom scallops are ranked Best Choice, while on-bottom scallops, which are dredged, are a Good Alternative when suspended culture scallops are not available.
2
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Table of Sustainability Ranks Sustainability Criteria
Low
Use of Marine Resources
√
Risk of Escaped Fish to Wild Stocks Risk of Disease and Parasite Transfer to Wild Stocks Risk of Pollution and Habitat Effects Management Effectiveness
√
Conservation Concern Moderate High
Critical
√ China, using wild-caught spat
√ √ off-bottom
√ dredged √ China and Japan
About the Overall Seafood Recommendation • • •
A seafood product is ranked “Avoid” if two or more criteria are of High Conservation Concern (red) OR if one or more criteria are of Critical Conservation Concern (black) in the table above. A seafood product is ranked “Good Alternative” if the five criteria “average” to yellow (Moderate Conservation Concern) OR if four criteria are of Low Conservation Concern (green) and one criteria is of High Conservation Concern. A seafood product is ranked “Best Choice” if three or more criteria are of Low Conservation Concern (green) and the remaining criteria are not of High or Critical Conservation Concern.
Overall Seafood Recommendation Off-bottom scallops: Best Choice
Good Alternative
Avoid
Good Alternative
Avoid
On-bottom (dredged) scallops: Best Choice
3
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Introduction Most concerns about the possible negative environmental impacts of aquaculture have focused on culture of freshwater and marine fish in cages, flow-through systems, and ponds, and the production of marine shrimp in ponds (Goldburg and Triplett 1997; Naylor et al. 2000). There has been much less discussion of the potential negative effects of the culture of bivalve shellfish as a result of the comparatively low impacts of producing them. Bivalves are filter feeders that obtain their nutrition by removing suspended particles from water. Because it is not necessary to apply feeds to stimulate production, bivalve farming does not increase nutrient inputs to coastal waters. In fact, an increase in abundance of shellfish in an area is usually considered to have a positive benefit on water quality (Shumway et al. 2003). Bivalve aquaculture includes the production of oysters, clams, mussels, and scallops. Statistics from the United Nations (UN) Food and Agriculture Organization (FAO) reveal that scallops are a popular seafood item and the harvest of scallops from the sea cannot meet the demand. The culture of these organisms increased from 975,000 metric tons (mt) in 1993 to nearly 1.2 million mt in 2003, to account for about 59% of world scallop production. Shumway et al. (2003) discussed the environmental virtues of bivalve culture in comparison to other types of aquaculture. They state that bivalve aquaculture has great potential for increasing seafood production without causing negative environmental impacts. Scallops are an expensive and increasingly-popular member of the bivalve group. There is rapid expansion of the scallop aquaculture industry and as demand grows, production practices in countries from which the United States imports need to be better understood. Basic biology Scallops are of the class Bivalvia, order Pterioida, and family Pectinidae. There are more than 360 species of scallops worldwide, and approximately 15 of these are used for aquaculture (Spencer 2002). Proportions of cultured scallop species produced globally are presented in Figure 1.
Figure 1. Global proportions of the main scallop species produced by aquaculture. Source: FAO 2005.
4
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
In the bay scallop (Argopecten irradians) (Figure 2), the labeum is situated at the end of the gill and is composed of a pair of labial palps on each side. The mouth appears to be split in the center of two labial palps and is connected to the esophagus. The flat oval-shaped stomach is connected to the esophagus at its upper end and to the intestine and rectum at its lower end. The rectum passes through the ventricle and goes downward along the back of the adductor muscle and turns to form the anus. The crescent-shaped gonad usually is located between the posterioventral part of the foot and the front side of the adductor muscle.
Figure 2. The bay scallop (Argopectens irradians). Image credited to Tampa Bay Watch.
Food is filtered by the gills and then sent to the mouth by movement of the labial palps. Food ingested by scallops is composed of phytoplankton, zooplankton, bacteria, and detritus. Under normal living conditions, the two shells of a feeding scallop are slightly open and the tentacles on the edge of the mantle are extended. If environmental conditions become unsuitable, the young scallop is capable of cutting off its byssus and swimming to a better location by means of a water-jet generated by the closing and opening of its shells. Scallops can swim faster than any other species of bivalves. When it finds a suitable place, it secretes a new byssus and attaches to the substratum again. The ability to secrete the byssus is determined by the size of the scallop and the water temperature. After it has grown up, the bay scallop discards its byssus. Scallops usually discharge sperm before releasing eggs. Mature sperm are smaller than eggs and swim actively in seawater where fertilization takes place. The embryo gradually develops into a free-swimming, ciliated larva called a veliger. During this stage the shell is secreted and the larva becomes a D-shaped pediveliger. At this stage, the larvae (often called crawlers) have both a functional velum and a foot, and alternately swim about and crawl on the bottom or other substratum. After a few days of crawling, the swimming ability of larvae gradually is reduced until the velum is completely reabsorbed and they must settle. Once settled, organs such as foot, velum and eye spot degenerate, and the gill and adductor muscles develop quickly. The early developmental stages of scallops are depicted in Figure 3.
5
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Figure 3. Developmental stages of the bay scallop (Argopecten irradians). Image credited to the Florida Fish and Wildlife Conservation Commission.
Aquaculture production Aquaculture has become a more important source of scallops than wild catch in many countries (Figure 4). According to FAO (2005), scallops are currently produced in 20 countries, the leading producer of which is China, followed by Japan, Chile, and Peru (Figure 5). China has in the past been the major producer of all types of bivalves, but Japan has provided most of the major advances in scallop aquaculture technology. Chile and Peru have been diversifying their aquaculture production since the late 1970s, and scallops have proven to be a profitable export.
Production (mt x 100,000)
25 Aquaculture Capture
20 15 10 5 0 1991
1994
1997
2000
2003
Figure 4. Comparison of scallop aquaculture and wild capture of scallops. Source: FAO 2005.
The two most valuable species of scallops produced in China are the Zhikong scallop (Chlamys farreri), which is native, and the Yesso scallop (Patinopectin yessoensis). The Zhikong and Yesso scallops are cultured in cool waters of the Bohai and Yellow Seas in northern China, while 6
MBA_SeafoodWatch_FarmedScallops_FinalReport
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to a lesser degree the bay scallop is cultured in warmer waters along the mid section of China’s coastline. The Yesso scallop was transplanted from Japan to China and the bay scallop is native to North America. Culture of these species using wild-caught seed and Japanese technology began in the 1960s (Spencer 2002). Scallop culture increased and hatcheries were introduced to enhance the spat supply. From 1993 to 2003, scallop production in China increased five-fold, though during that time period there were dramatic fluctuations in production. For example, production decreased from 1,000,000 mt in 1997 to 629,000 mt in 1998 as the result of mass mortalities during the summer. Gosling (2003) attributed these die-offs to over-crowding, high water temperatures, and deteriorating water quality. In Japan, the central government has provided significant funding for the advancement of scallop aquaculture. Japanese scallop farming dates back to 1936 in North Hokkaido; however, scallop farming was not successful until the late 1960s. The main species cultured in Japan is the Yesso scallop. Initially, only bottom culture was conducted along the coast of Hokkaido, and presently bottom culture still accounts for over half of the production in this area. Suspended culture of scallops is common in Mustso Bay in northern Aomori. Ear-hanging of scallops was very popular in the 1980s, but production by this technique has declined because of excessive fouling. Scallop production in Japan also fluctuated during the period 1993 to 2003. Production peaked at 265,000 mt in 1996 and then decreased annually until it reached 210,000 mt in 2000. Production increased in 2003 to 258,000 mt. The main culture species in Chile is the Chilean/Peruvian scallop (Argopecten purpuratus). The scallop industry in Chile was established in the late 1970s, and it has become a profitable component of the nation’s aquaculture industry. Much of the production in Chile has been aided by Japanese overseers. The main areas of production are the Mejillones, Tongoy, and Herradura Bays in northern Chile. Spatfalls are irregular and the country is reliant on hatcheries for spat. Grow-out of spat to market size is conducted using Japanese lantern nets and ear-hanging techniques. The Chilean scallop industry produced a high of 21,000 mt in 1999, but production declined to 15,000 mt in 2003. Production in Chile has been hindered by insufficient spatfalls and excessive fouling.
7
MBA_SeafoodWatch_FarmedScallops_FinalReport
July 20, 2006
Production (mt x 10,000)
140 120 100
China Japan Chile Peru Others
80 60 40 20 0 1991
1994
1997
2000
2003
Figure 5. The major countries producing scallops by aquaculture. Source: FAO 2005.
Peru’s scallop industry developed from the natural fishery. Divers retrieving scallops for sale sold undersized scallops to farmers for further grow-out. This progressed to the adoption of traditional scallop culture in Peru. The main species produced in Peru is Argopecten purpuratus. Seed is obtained from the wild using spat collectors, and grow-out is performed using hanging culture techniques. Peruvian scallop farming is centered on the Bay of Paracas where the seabed is leased from the Department of Fisheries and the Department of Navy. The Peruvian industry has grown more slowly than that of other major scallop-producing countries. Production in Peru was between 100 and 500 mt during the period 1993-1997. Production has increased, and in 2003, about 6,700 mt of scallops were produced. The increase in production can be attributed to refinement in culture techniques. Moreover, a higher price can be obtained for Peruvian scallops when there is low capture of the Calico scallop (Argopecten gibbus) in Florida. The global value of scallops reached $1.8 billion in 1997 (Figure 6), but declined drastically in 1998 as a result of the decreased production in China. Since 1998, the value of scallops from aquaculture has continued to increase each year and was $1.7 billion in 2003.
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Value (USD x billions)
2.5 2.0 1.5 1.0 World Scallop Value
0.5 0.0 1992
1994
1996
1998
2000
2002
2004
Figure 6. The economic value in billions of U.S. dollars (USD) of world scallop production. Source: FAO 2005.
FAO (2005) data reveals that there is relatively little production of scallops by aquaculture in the United States, but capture of scallops in U.S. waters is approximately 207,000 mt. Of this quantity roughly 7,000 mt is exported (FAO 2005). Thus, the U.S. consumes 200,000 mt of captured scallops from U.S. waters and 23,580 mt from imports, which include a combination of cultured and wild-caught scallops. Data on the fraction of scallop imports produced by aquaculture internationally is not readily available, but estimates of this fraction can be calculated using a combination of U.S. trade data and FAO aquaculture and capture fisheries statistics (Table 1). From these estimates a rough idea of the quantity of scallops produced by aquaculture and by which country can be tallied. U.S. imports of scallops produced by aquaculture are estimated at 8,304 mt or roughly 35% of all scallops imported. Yet when compared to total scallops consumed in the U.S., scallops imported and produced by aquaculture represent only 3.7%. Thus, over 96% of all scallops consumed in the United States are captured from the wild. Although these estimates reveal that few farmed scallops are consumed in the United States, there is a fraction of scallop imports which are produced by aquaculture. The overwhelming majority of these imports originate in China and Japan (Table 1).
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Table 1. U.S. imports of scallops produced by aquaculture and country of origin for 2003 (USDA FAS 2005; FAO 2005). Percentage of aquaculture production calculated using FAO statistics on aquaculture and capture production of scallops for individual countries. Note: Quantity of scallop aquaculture imports estimated by fraction of individual countries’ percentages of scallop aquaculture and does not represent actual value of U.S. imports of scallops produced by aquaculture. U.S. scallop import quantity (mt)
Percentage of export country aquaculture production of scallops
Estimate of scallop imports by aquaculture (mt)
Australia
1
